ИСТИНА

Catalysts have been received by annealing in the atmosphere of air of mixed nitrates Bi, Mg and Cu at 700-720°C. The crystal phase of freshly prepared catalysts were identified by methods: XRD, SEM, XPS. XRD data showed that the catalyst based on Bi-Mg consists of phases Bi12MgO19 and MgO; based on of Bi-Cu-Mg, consists of phases Bi12MgO19 and Cu4MgO5 while the catalyst based on of Bi-Cu is presented only by one phase CuBi2O4. With the help of SEM it is revealed that received catalytic systems crystallize in the form of aggregates. The surface of aggregates for all catalysts is smooth (candy like). The sizes of formed aggregates is in the range 0-1000nm while most mass of aggregates is in the range 200-600nm. Before and after soot oxidation in presence of Bi-Mg, Bi-Su-Mg, Bi-Cu in XPSs detected are Bi 4f 7/2 (158.7eV), Mg 2p (49.6, 49.7, 49.8eV) and Cu 2p 3/2 (933.3eV) lines which bond energies are identical to freshly prepared samples without soot. This corresponds to Bi3+, Mg2 + and Cu2+ oxidation levels. This gives evidence that in the process of soot catalytic oxidation the change of oxidation level of the elements forming catalytic system is not observed. From XPS it, as well, follows that oxidation of soot in presence of Bi-Mg additive strongly saturates soot surface with oxygen - С/О ratio equals to 8.3. In case of soot oxidation without additive the concentration of oxygen on a surface falls-off: (С/О = 40). Experiments on detection of catalysts activity in soot oxidation with oxygen were run with the help of molecular oxygen containing microamount of water in flow-through microcatalytic reaction cell at 300-580°C in pulse mode with immediate evaluation by chromatograph of CO2 and CO. Samples of mixtures soot-catalyst were prepared with mass ratio 2:1. The catalysts activity based on Bi in oxidation of diesel soot with oxygen was identified. The temperature of soot oxidation start corresponds to 340°C for all catalysts. The catalytic activity jump observed at 400.С. The series of catalysts’ activity in soot oxidation with oxygen is as follows: Bi-Mg > Bi-Cu-Mg > Bi-Cu. Correlation between catalytic activity of the system and its ability to saturate the surface of soot with oxygen is noted. The Bi-Mg system found to be more stable in soot oxidation with oxygen in comparison with all other studied catalysts. It is supposed that catalytic action of the studied systems at soot oxidation with oxygen can be connected with their enhanced ability to initiate and facilitate saturation of a surface with oxygen as well as formation and disintegration to CO and CO2 of various surface oxygen-containing functional groups.